The present invention relates to antifriction bearings comprising an inner race, an outer race having an outer peripheral surface to be brought into contact with other member for use as a roll, and rolling elements arranged between the inner and outer races, and to a process for producing an outer race for use in antifriction bearings.
The outer races of antifriction bearings are used, for example, as backup rolls in multistage rolling machines. Such antifriction bearings are generally used with a lubricant containing extraneous matter becoming mixed therewith. An elongated rolling fatigue life is of course required of these antifriction bearings for use under the lubricating conditions involving the use of a lubricant containing extraneous matter, while also required are the resistance of the outer race to breaking and the resistance of the outer race to plastic deformation due to the heat of or load on the outer race, because if the outer race breaks, the rolling line must be brought out of operation, and because the plastic deformation of the outer race impairs the quality of the rolled product. The rolling line is usually inspected periodically in order to avoid the stoppage of the line or the degradation of the rolled product, and the rolling bearings are replaced before becoming damaged or broken.
However, when the outer race of the antifriction bearing for use as a backup roll breaks or undergoes plastic deformation within a short period of time, there is a need to perform the periodic inspection in relatively short cycles and the inspection requires cumbersome work.
To prevent the breaking or plastic deformation of outer races, an outer race blank prepared from a bearing steel in a predetermined shape is conventionally carburized or carbonitrided to form a hardened surface layer of relatively great hardness over the outer periphery of the outer race and to impart toughness to the portion of the race inwardly of the surface layer.
The antifriction bearing having an outer race for use as the backup roll in multistage rolling machines is a bearing of high load capacity, and the outer peripheral surface of the outer race, if defaced, must be ground again to remove the defacement, hence the necessity of giving an increased thickness to the hardened surface layer.
The hardened surface layer having an increased thickness and formed by a carburizing or carbonitriding treatment nevertheless has the problem of requiring an elongated treating time and an increased production cost.